The present invention relates to an image display device such as liquid crystal projector having a theft prevention function.
Image display devices, such as a liquid crystal projector, have become popular. A liquid crystal projector is compact, easy to carry, and relatively expensive. As a result, theft of liquid crystal projectors is increasing. This has increased the need for theft prevention measures.
Theft prevention measures include the setting of passwords or the use of PC cards so that a liquid crystal projector has a theft prevention function or the attachment of a theft prevention device to the liquid crystal projector.
Japanese Laid-Open Patent Publication No. 7-160955 discloses a theft prevention device connected to a liquid crystal projector by a multi-core cable. More specifically, the theft prevention device includes an alarm control device and an alarm device. The alarm control device is connected to the liquid crystal projector by a multi-core cable including a plurality of signal lines. The alarm device is connected to the alarm control device and receives a theft detection signal generated by the alarm control device. The alarm control device generates the theft detection signal, and sends the theft detection signal to the alarm device when the multi-core cable is cut or when the liquid crystal projector is disconnected from the multi-core cable to carry away the liquid crystal projector. The alarm device generates a warning such as buzzing sound.
However, in the conventional theft prevention device, the function of the theft prevention device, that is, the alarm function of the alarm device is valid from when the device is shipped out of a factory to when the user starts use. Therefore, the theft prevention function may be erroneously activated after the alarm device is shipped out of the factory and before the user starts use (e.g., when packaging or transporting the theft prevention device). In such a case, a warning such as buzzing sound is given off even though theft of the liquid crystal projector has not occurred. This creates undesirable noise.